The present invention relates to a high molecular composition, the radiation resistance being improved drastically, and an electric wire or cable used said high molecular composition as a covering material.
Organic high molecular materials used for nuclear reactors, breeder reactors, treatment facilities of radioactive wastes, ionizing radiation generator or the like, for example, electric wires, cables and various instruments are always exposed to radiation to a considerable extent.
Such high molecular materials having been subjected to the exposure of high doses of radiation in the air generally become hard and brittle to lose the pliability and to weaken, so that the characteristics thereof are lowered remarkably.
For this reason, high degree of radiation resistance is requested for the high molecular compositions used for the covering and insulating materials of electric wires, cables, etc., packings, seal materials, frames, hose materials, etc. having such purpose of use from the standpoints of economics and safety, and the researches on the technology to provide the radiation resistance to high molecular materials are advancing.
It has been known that, by formulating a halogenated acenaphthylene and/or condensates thereof represented by a following general formula [I] ##STR3## (wherein X indicates a chlorine or bromine atom, a indicates 0 to 2, b indicates 1 to 6 and n indicates an integer not less than 1) to the high molecular polymer, high degree of radiation resistance and excellent fire resistance can be provided to the high molecular polymer (Japanese Patent Publication No. Sho 58-1146 and Sho 60-25063).
When formulating said halogenated acenaphthylene and/or condensates thereof to the high molecular polymer, said halogenated acenaphthylene and/or condensates thereof are used usually by allowing to melt and disperse into the high molecular polymer by heating at the time of kneading or thermal molding.
As an another method, utilizing the radical polymerization reaction of double bond between carbon 1 and carbon 2 of halogenated acenaphthylene unit, free radical-generating treatment is carried out after the molding to graft onto the high molecular polymer. It is known that the improvements in the radiation resistance and the fire resistance of high molecular polymers can be achieved by these methods.
As a result of investigations on the effect of provision of radiation resistance to the high molecular polymer by the use of halogenated acenaphthylene and/or condensates thereof, the inventors have found that there occurs a significant difference in the development of radiation resistance depending upon the fluctuation of processing conditions, difference in quality of halogenated acenaphthylene and/or condensates thereof and the like.
Namely, when the halogenated acenaphthylene and/or condensates thereof were formulated to polyolefinic resins, rubbers, etc., if the processing temperature was lower than the melting temperature of halogenated acenaphthylene and/or condensates thereof, or if the condensation composition of condensates of halogenated acenaphthylene was high, such a phenomenon that the elongation ratio at the fracture point being a judging criterion of radiation resistance was lowered was recognized resulting in the problem.
Moreover, in consequence of the investigations on the application of high molecular compositions formulated the halogenated acenaphthylene and/or condensates thereof to the use for a nuclear reactor, that the hot-water resistance proved poor. Namely, when these high molecular compositions were exposed to the high-temperature steam of 150.degree. C. for more than 24 hours, the mechanical properties were kept, but the sheet swelled and that the electric properties, in particular, the dielectric breakdown voltage was lowered.
In addition, when formulated to crosslinked polyethylene, there were such problems that the crosslinking of polyethylene was hindered not to raise the gel fraction and to cause a decrease in the deformation temperature under heat and such processing problems that the surface of sheet was roughened at the time of press molding and the like.
Furthermore, as a designing standard of nuclear power station, loss of coolant accident (LOCA) is established. The requirement matter states that it is necessary for the high molecular polymers to retain their good electric characteristics even if exposed to heated steam or hot water after the exposure to radiation. However, with those of which the elongation ratio at the fracture point was lowered after the exposure to radiation as described above, it was also recognized that the electric characteristics were lowered after the exposure to steam. In other words, even after bromine was eliminated through the exposure to radiation and the brominated acenaphthylene and/or condensates thereof became to a stabilized state, the phenomenon that the electric characteristics were lowered remarkably by super heated steam or hot water was recognized to become a problem.
The purpose of the present invention is to provide a high molecular composition stably developable the high-degree of radiation resistance, hot-water resistance and excellent electric characteristics after the LOCA test by being not subjected to the influence of fluctuation of processing and molding conditions and by suppressing the influence of quality of halogenated acenaphthylene and/or condensates thereof.
In view of these problems of the prior art, the inventors made diligent investigations on the method of developing the radiation resistance of high molecular composition formulated the halogenated acenaphthylene and/or condensates thereof. As a result, the inventors have found that, depending on the processing and molding conditions and the difference in the quality of halogenated acenaphthylene and/or condensates thereof, the dispersibility and the compatibility in the high molecular polymer differ subtly to affect significantly on the development of various characteristics.
In order to solve this problem, the inventors energetically searched for additives not affecting adversely on the physical properties of the high molecular compositions, such as an improver of dispersibility to improve the dispersibility of halogenated acenaphthylene and/or condensates thereof, and a trapping agent of hydrogen halide formed by de-halogenation.
As a result, various kinds of high molecular resins, rubbers, ester plasticizers, paraffinic and aromatic process oils, various lubricants,.etc. proved to hardly improve the dispersibility and, in the case of the formulation of metal oxides such as zinc white, magnesium oxide, antimony trioxide, etc. caused swelling by hot water and did not prevent the lowering in electric characteristics.